Surface preparation, such as cleaning, etching, and stripping, is an essential and important element of the manufacturing process for semiconductor wafers and similar workpieces. Surface preparation steps are commonly performed, using liquid corrosive, caustic, or solvent chemicals, or using vapor phase chemicals. Surface preparation of workpieces is performed to prepare or condition the surface for a subsequent process step.
Cleaning is a critical step in manufacturing semiconductors and similar products. Cleaning involves the use of chemical formulations to remove contaminants, such as oxides, particles, metals, or organic material, while maintaining the cleanliness and integrity of the surface of the workpiece. Some liquid, gas or vapor phase chemicals when applied to a workpiece, result in surface characteristics that are more susceptible to contamination than others. For example, application of hydrofluoric acid (HF) to the surface of a workpiece will remove oxide from the silicon surface, resulting in a surface that is active. Workpieces in general, and especially workpieces having an active surface, are constantly susceptible to contamination by airborne microscopic particles. Contamination can also occur in the cleaning process, when the liquid process media is removed from the surface of the workpiece.
Thus, to minimize contamination of the workpiece, it is advantageous to perform a sequence of surface preparation steps within a controlled environment, that preferably occupies a relatively small amount of fabrication facility space, and in which exposure to contamination sources is minimized. Accordingly, it is an object of the invention to provide improved surface processing methods and apparatus.
Cleaning workpieces while avoiding or minimizing contamination has long been an engineering challenge. Workpieces are often cleaned with a spray or bath of de-ionized water. The water is then removed, often in the presence of an organic solvent vapor, such as isopropyl alcohol, which lowers the surface tension of the water. This helps to prevent droplets of water from remaining on and contaminating the workpiece.
Various cleaning methods and systems and various rinsing and drying methods and apparatus have been proposed and used. In a typical system, wafers are immersed in a vessel. A mechanism is provided to hold the wafers. Another mechanism is provided to lift the wafers out of the liquid, by pushing them up from below. While this technique has been used, it can result in trapping of liquid in or around the spaces where the wafers contact the holding mechanism, resulting in increased contamination. It is also complicated by the need for the lifting mechanism. In an alternative system, the wafers are held in a fixed position while the liquid is drained away from below. This technique has less tendency for trapping liquid. However, as the liquid level drops, the solvent vapor above the liquid is absorbed by the liquid. Consequently, the top sections of the wafer are exposed to liquid which is different from the liquid at the bottom sections of the wafers. This potentially results in non-uniform processing. Accordingly, while these and other techniques have been used with varying degrees of success, there is still a great need for improved systems and methods for cleaning workpieces.
It is therefore also an object of the invention to provide an improved system and method for cleaning workpieces.